National Highways have apologised after “unexpected issues” caused an outage which left motorists seeing random lane closures on smart motorways.

Issues were reported on the M6, M1 and A1(M) on Wednesday, with signs reportedly encouraging road users to change lanes “constantly” while some signs were so bright they “hindered night vision”.

Campaigner Claire Mercer, whose husband Jason Mercer died after stopping on a smart motorway in South Yorkshire, told the PA news agency she had been contacted by those operating the gantries who said it was “the worst outage they had had”.

She said: “I started getting emails, first of all I got one at 8pm last night, then 10, then 11, just from different people… saying ‘it’s still out, we still can’t control things, it’s across five counties’.

“Basically people are just at their wits’ end.”

Motorists complained on Twitter about the signs on the gantries, complaining about red ‘X’ signs for “mile upon mile” on lanes on the A1(M) and “unreadable” overhead signs and incorrect lane closures on the M6.

Addressing what whistle-blowers had told her about how they dealt with the problem, Ms Mercer told PA: “One contact said to me… that they were just sending traffic officers to black spots, basically to where people were more likely to die.

“There were traffic officers there because they couldn’t detect vehicles, they couldn’t control the signs, so the only thing they could do was have traffic officers waiting – which is pretty horrible to hear.

“Yesterday one of the sources said they couldn’t control the signs themselves at all and that random signs were popping up.

“So it wasn’t just that they couldn’t put their messages on – unwanted messages were appearing across the system.”

Ms Mercer said those who had contacted her did not know what was wrong with the system, saying they were “out of options now”.

In response, National Highways operational control director Andrew Page-Dove said: “We apologise for any inconvenience caused by a planned outage of our signs and signals technology yesterday (Wednesday) afternoon and evening. The outage was in response to unexpected issues.

“As with any technology, there are occasional outages and so we have well-rehearsed procedures to deal with issues which arise.

“We took additional measures to limit any impact on drivers or traffic flow, including extra traffic officer patrols and, virtual CCTV patrols.

“We took the decision to reset the systems to ensure any errors were rectified as swiftly as possible.”